HEBER CITY — Seventeen students and a teacher were treated at a local hospital Tuesday after a carbon monoxide scare at Heber Valley Elementary School.

All 18 have been released, said hospital spokeswoman, Amy Tuddenham.

The school's 550 students were not let out of school until around 5 p.m., after they all could be tested with carbon monoxide monitors at the school, according to Wasatch County Fire Department Lt. Janet Carson.

Students expressing symptoms of elevated carbon monoxide — headaches and stomach aches — were tested first.

School officials decided it would be too unmanageable to release a few children from school at a time, Carson said.

The incident was apparently caused by construction equipment being used to build additional classrooms, she said. Carbon monoxide exhaust had entered through a side door, setting off the school's smoke alarms around 10:30 a.m.

At that time, the school was evacuated and the fire marshal checked carbon monoxide levels throughout the building, where it was found only between the two sets of double doors at the side entrance, Carson said.

However, several hours later, children began complaining of stomach aches and headaches and Wasatch County Fire, EMS and health department officials responded to the school to check students and staff with the monitors.

The monitors are similar to oximeters used to test for blood oxygen levels and take around 30 seconds to a minute per test. 

Those with elevated levels were transported by car and ambulance to Heber Valley Medical Center around 4:45 p.m. Concerned parents brought in additional children on their own, Tuddenham said.

Construction has been halted at the school until the safety of students and staff can be assured, Carson added. Classes will be held as usual Wednesday.